An inkjet printer typically includes one or more cartridges that contain ink. In some designs, the cartridge has discrete reservoirs of more than one color of ink. Each reservoir is connected via a conduit to a printhead that is mounted to the body of the cartridge. The reservoir may be carried by the cartridge or mounted in the printer and connected by a flexible conduit to the cartridge.
The printhead is controlled for ejecting minute drops of ink from the printhead to a printing medium, such as paper, that is advanced through the printer. The printhead is usually scanned across the width of the paper. The paper is advanced, between printhead scans, in a direction parallel to the length of the paper. The ejection of the drops is controlled so that the drops form images on the paper.
The ink drops are expelled through nozzles that are formed in a plate that covers most of the printhead. The nozzle plate may be bonded atop an ink barrier layer of the printhead. That barrier layer is shaped to define ink chambers. Each chamber is in fluidic communication with and is adjacent to a nozzle through which ink drops are expelled from the chamber. Alternatively, the barrier layer and nozzle plate can be configured as a single member, such as a layer of polymeric material that has formed in it both the ink chambers and associated nozzles.
The mechanism for expelling ink drops from each ink chamber (known as a “drop generator”) includes a heat transducer, which typically comprises a thin-film resistor. The resistor is carried on an insulated substrate, such as a silicon die. The resistor material layer is covered with suitable passivation and cavitation-protection layers.
The resistor has conductive traces attached to it so that the resistor can be selectively driven (heated) with pulses of electrical current. The heat from the resistor is sufficient to form a vapor bubble in each ink chamber. The rapid expansion of the bubble propels an ink drop through the nozzle that is adjacent to the ink chamber.
Many of the components of the drop generators are fabricated or processed in ways that include photoimaging techniques similar to those used in semiconductor device manufacturing. The components are incorporated into and carried on a front surface of the rigid silicon substrate. The front surface of the substrate is also shaped by etching to form a trench in that surface. The trench is later connected with a slot that is cut through the back of the substrate so that liquid ink may flow from the reservoir, through the connected slot and trench, and to the individual drop generators.
The trench that is etched in the substrate surface is located adjacent to the drop generator components. Also, the silicon etching that forms the trenches takes place after some or all of the drop generator components have been added to the substrate. Therefore, it is important to form the substrate trenches in a manner that does not damage drop generator components. In this regard, the portion of the silicon substrate that is etched must be carefully defined on the substrate. This definition may be accomplished by masking the area to be etched with material that resists the effects of the etchant that is used for etching the trenches in the silicon. Moreover, production efficiency requires that this masking task be accomplished with minimal interference with, or delay in carrying out, the steps associated with producing the thermal inkjet printhead.